I am under NDA...but it is a 1500m concept spaceship for a well known space agency. So you can imagine the scale, and the detail needed (i modeled even the windows).
I was thinking of just importing sections and texture that. The renders are 6k and closeup so i need the high resolution. 50m polys sounds like a lot, but the geometry is pretty lightweight, because it iss solid surfaces there are a lot of hidden polygons that could be deleted.